I realize that some people have been taught that symbols are to be kept secret.  While this may be the case in other disciplines, I have found that to many Japanese students, this is not the case.  All the traditional symbols are now known to be derived from other sources in Japanese culture, and can be found in their spiritual books or temples.

From the original Usui-Do teachings, we know that the symbols originated in Chinese Taoism where they are still taught today.  Usui Sensei used them as part of the spiritual training he was presenting.  They each represent a facet of your being that can be awakened by you - Focus, Harmony, Connection (to other aspects of you through time and space) and Empowerment (connecting to a higher level of your being). They were originally referred to as just symbol, #1, 2, 3 or 4. and were taught in a from of kata or meditative exercise, only used in class.  No attunement to them was given.  The Japanese version of the special word or kotoba for each symbol is different than the original Chinese.

The symbols were not applied to others, although Dr. Hayashi seemed to experiment with this.  The original Reiki society - URR Gakkai - dropped the use of the symbol itself and simply created a mantra (modified from the original kotoba or word) to help focus on this aspect of Reiki. They taught that the symbols are part of each Reiki Reiju (attunement) experienced - right from Shoden - and thus their own Reiju did not include any of the symbols.  As well, their healing work does not include symbols - it seems that the effects of each are expected to be automatically presented to a recipient if it is called for.  Hence in a technique like Sei Heki Chiryo-ho, you will notice that the symbol is not drawn or called upon.  Again, it seems Dr. Hayashi was the one to make use of these in individual reiju or attunements, and in healing work.

In the August 1999, Japanese Reiki Master Hiroshi Doi offered his own explanation, saying that in the Original Reiki Society(URR Gakkai) the symbols are no longer used.  They may be shown for their historical value, but students are expected to simply use the energy they are given in empowerments at Okuden and Shinpiden level.  Note that the Gakkai would only share additional energies and techniques (Okuden) if you could demonstrate your abilities to sense disease in the body.  Then it was felt you could appreciate the additional skills. 

Today in the Usui Reiki Ryoho Gakkai  you can wait up to 10 years before you are allowed to receive Okuden (I understand this may be decreased). At this point, if you are still unable to demonstrate the required abilities, you are then granted Okuden more as an honorific.

According to Doi-sensei, the Gakkai explains that the "symbols" were first introduced by Usui-sensei as a form of training wheels for some students. They say that Sensei discovered that some students were unable to accept that the energies they received beyond the Reiki energy could be transmitted just by will. And so to assist one student with distant Reiki, he had the person focus on an old Buddhist mantra, which Dr. Hayashi came to teach as the Connection energy.  This eventually spread to the other 3 main energies shared by Sensei as well.  Sensei obviously drew on his previous research in order to provide an appropriate mantra or symbol. See the URR Gakkai method for Distant Reiki or Enkaku Chiryo-ho here.  Note that the symbols are not drawn but the first 3 are simply combined intentionally.

Doi-san points out that even training wheels can get in the way after awhile as you improve your abilities, for they may come to inhibit your progress.  (e.g. how fast can you travel or turn corners?) He acknowledges that in the west, many may have sought to have bigger and more impressive training wheels, although he recognizes the use and importance of personal symbols. 

In Dr. Hayashi's more structured form of Reiki, Usui Shiki Ryoho (Usui Method of Healing), the use of the symbols seemed to become solidified into a standard part of the training, and if at any point they were later de-emphasised, this was not passed on by Mrs. Takata in the west. Thus the symbols grew in importance along side the energy they convey.

Some students are taught that symbols are sacred.  I have learned that people are sacred, not symbols.  The symbols (which act as yantras or a visual focus) and their mantras or names (which act as an audio focus) are simply aids to concentrate on when you wish to connect and work with specific vibrations or frequencies of energy from within.  In some energy disciplines I have learned, once the student knows the energy they wish to connect to, simply thinking of the energy creates the connection or awareness.  This can be true of Reiki symbols.

Since the traditional symbols have been misrepresented over and over, perhaps it is time to teach them to all in their original form.  It is quite beneficial to experience these within the framework of an attunement, as the Reiki teacher helps you to pay attention to each specific aspect of them.  So in a way it can short cut a longer approach of trying to sense them on your own.